A size-dependent crystal plasticity finite-element model for creep and load shedding in polycrystalline titanium alloys

A rate-dependent anisotropic elastic-crystal plasticity based finite-element (FE) model with size-dependent yield strength is developed for polycrystalline Ti-6242. The initial slip system deformation resistances in the crystal plasticity relations are expressed as Hall-Petch type relations, where the grain size, lath size and colony size are chosen as characteristic lengths depending on the nature of slip. The FE model incorporates accurate phase volume fractions and orientation distributions that are statistically equivalent to those observed in orientation imaging microscopy (OIM) maps of the microstructure. The model is validated with experimental results on constant strain rate and creep tests. A relationship between the macroscopic flow stress and grain size and lath size for two-phase Ti-6242 is proposed. The effect of grain morphology on creep-induced load shedding and localization is discussed. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.